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The effect of core segregation on the Cu and Zn isotope composition of the silicate Moon

Y. Xia1,

1CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China

E.S. Kiseeva2,3,

2Department of Earth Sciences, South Parks Road, Oxford OX1 3AN, UK
3University College Cork, School of Biological, Earth and Environmental Sciences, Cork, Ireland

J. Wade2,

2Department of Earth Sciences, South Parks Road, Oxford OX1 3AN, UK

F. Huang1

1CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China

Affiliations  |  Corresponding Author  |  Cite as  |  Funding information

Xia, Y., Kiseeva, E.S., Wade, J., Huang, F. (2019) The effect of core segregation on the Cu and Zn isotope composition of the silicate Moon. Geochem. Persp. Let. 12, 12–17

NERC grant NE/L010828/1 to E.S. Kiseeva
NERC grant NE/K009540/1 to J. Wade
Strategic Priority Research Program (B) of Chinese Academy of Sciences (Grant No. XDB18000000) to F. Huang
National Science Foundation of China (41325011, 41630206) to F. Huang

Geochemical Perspectives Letters v12  |  doi: 10.7185/geochemlet.1928
Received 02 July 2019  |  Accepted 24 September 2019  |  Published 19 November 2019
Copyright © The Authors

Published by the European Association of Geochemistry
under Creative Commons License CC BY-NC-ND 4.0

Keywords: lunar isotopes, lunar formation, elemental volatility, experimental petrology, lunar core formation, sulfide-silicate isotopic partitioning




Figure 1 Half-mass condensation temperatures (Lodders, 2003) for a solar system composition gas versus isotope composition. Data reference for the isotopic compositions are detailed in the Supplementary Information. It should be noted, however, that the condensation temperatures displayed are for deposition from gas to solid in a nebula gas, not for evaporation from a liquid at the more oxidising conditions pertinent to Moon formation.
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Figure 2 (a,b) Zn and Cu isotope fractionation factors between liquid metal-silicate and sulfide-silicate as a function of temperature. Both increasing temperature and Ni content of sulfide decrease the Zn and Cu isotope fractionation, with the result that low Ni sulfides all exhibit a temperature dependent excess of isotopically light Cu and Zn. The pale-red band is the 95 % confidence interval for the regression shown.
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Figure 3 The Cu isotope evolution of the silicate Moon during lunar sulfide segregation. Assuming the Moon is derived from the precursor BSE, and the Moon’s core is predominantly FeS (equating to a bulk Moon of ~7500 ppm S), or just the outer core (3500 ppm S) and sulfide sequestration occurs by Rayleigh fractionation, the silicate Moon becomes progressively lighter in Cu. Horizontal lines represent values of the BSM estimated by lunar basalts (red) and the BSE (green) (Herzog et al., 2009

Herzog, G., Moynier, F., Albarède, F., Berezhnoy, A. (2009) Isotopic and elemental abundances of copper and zinc in lunar samples, Zagami, Pele’s hairs, and a terrestrial basalt. Geochimica et Cosmochimica Acta 73, 5884-5904.

). The pale blue band represents 2 standard deviations of the error on the mean of the fractionation regression.
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Figure 4 Cu is hosted in lunar sulfides as a consequence of its significantly higher preference for the sulfide phase over silicate during LMO cooling and the consequent decreasing solubility of sulfide in the melt. Zn, however, is little affected implying the BSM Zn isotopic content is set by element volatility during Moon formation and LMO degassing. The BSM’s Cu isotopic composition reflects sulfide loss to the lunar core.
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